Quantum computing was theoretically developed by Feynman (Optics News, Feb. 1, 1985) and Deutsch (Proc. Royal Soc. London A400, 97 (1985)). Quantum algorithms for these theoretical machines were developed by Grover (Phys. Rev. Lett. 79, 4709 (1997)) to search unsorted databases faster than is possible with classical computers, and by Shor (Proc. 35th Ann. Symp. on Found. of Computer Science, IEEE Comp. Soc. Press, Los Alamitos, Calif. 1994) to factor numbers and calculate discrete logarithms. Early experimental implementations of quantum computers used ion traps (Cirac and Zoller, Phys. Rev. Lett. 74, 4091 (1995); Monroe et. al, Phys. Rev. Lett. 75, 4714 (1995)) and optical systems (Turchette et. al., Phys. Rev. Lett. 75, 4710 (1995)) but were able to implement only a single logic gate, one of many that would be required to implement an algorithm.
A significant theoretical advance in quantum computing came when the means for performing quantum computation using nuclear magnetic resonance (NMR) techniques was developed by Gershenfeld and Chuang (Science 275, 350 (1997)), and independently by Cory, Fahmy, and Havel (Proc. Nat. Acad. Sci. 94, 1634 (1997)). The NMR technique has successfully been used to demonstrate the operation of two-bit quantum algorithms for searching (Chuang, Gershenfeld, and Kubinec, Phys. Rev. Left. 80, 3408 (1998)) and period-finding (Chuang, Vandersypen, Zhou, Leung, and Lloyd, Nature 393, 143 (1998)).
To date, all of the efforts in NMR quantum computing (NMRQC) have involved the use of isotropic liquid solvents, into which molecules specifically suited for carrying out quantum computations are dissolved. Isotropic liquid solvents allow the molecules to tumble isotropically, and average the dipolar interactions to zero. The couplings among the spins that are required for quantum computation are thus scalar in nature. The use of isotropic liquid solvents in NMRQC also results in long coherence times, which means that there is a significant amount of time to perform a computation before external forces disrupt or affect the coupling of the nuclear spins. It has been understood that these features are highly desirable, and that solids, which have long range dipolar couplings, cause rapid decoherence and therefore offer only very reduced operation times when used for quantum computation (Chuang, Gershenfeld, Kubinec, and Leung, Proc. Royal Soc. London A (1988) 454, 447). Furthermore, it is known in the art that the advantages of using dipolar couplings in solids for NMRQC operations are outweighed by the disadvantages (W. S. Warren, Science 277, 1688, 1997).
However, the use of liquid solvents strongly limits the clock rate and thus the computation speed of NMR quantum computers because the requisite coupling among the nuclear spins that persists in solution, the so-called scalar coupling, is small. NMR quantum computers based on liquid solvents also require long waiting times between computations for reinitialization because of the long time required for buildup of the requisite longitudinal nuclear spin magnetization.
The use of liquid crystals as a solvent for NMR experiments was developed for retaining and extracting information from the dipolar interactions among nuclei in the dissolved molecules (A.Saupe and G. Englert, Phys. Rev. Lett. 11, 462 (1963). In contrast with isotropic liquid solvents, liquid crystal solvents impede the tumbling of dissolved molecules in such a way that the molecules become partially oriented. The result on the NMR spectra is that dipolar couplings between nuclear spins that are averaged to zero in isotropic liquid solvents are observed in liquid crystal solvents. However, liquid crystals have not been used as solvents for NMRQC. This is because it was believed that liquid crystal solvents which induce dipolar couplings would require unduly complex implementation of NMRQC algorithms.
What is needed is a NMRQC system that increases the computation speed and reduces the re-initialization time over NMRQC systems that rely on liquid solvents.